1. Field of the Invention
The present invention relates to a mobile phone with an encryption function, and more particularly to a mobile phone capable of connecting to an expansion memory to store a ciphered document and restricting a crypto-key used for decrypting the ciphered document from being stored in the expansion memory.
2. Description of the Prior Art
Widely available mobile communications is one of the distinctive hallmarks of modern information-based society. In order to improve the functions of the mobile phones, expansion slots are designed for connecting the mobile phones to additional devices. For example, a user can purchase an MP3 (Moving Pictures Experts Group Layer III Audio) module to plug in his/her mobile phone to enjoy MP3 quality music.
Moreover, the expansion memory card, such as a secure digital card (SD card), multi media card, smart media card, or compact flash card, etc., is one of the widespreadusages of the expansion modules for data storage purpose. Users can first use the expansion memory cards to store files, such as electronic books and MP3 files, and then uses their mobile phones to read or listen the books or the music. However, because the prior art mobile phones are improperly designed to protect the data stored in these expansion memory cards, the data stored in these memory cards may be stolen when the memory cards are lost. Moreover, if the users store their secrets, such as bank accounts and passwords, in the memory cards, they may have huge economic loss when the data stored in the memory card is stolen.
Among the various memory cards, the secure digital card (SD card) is a memory card with an encryption and decryption function. The SD card uses a pair of crypto-keys to encrypt and decrypt data. However, because the pair of crypto-keys is stored in a hidden area of the SD card and the operations for encryption and decryption of the SD card are performed by internal circuits of the SD card, the data stored in the SD card is not safe from hackers when the SD card is lost.